JPH03254448A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To miniaturize an entire optical system by providing an optical path separation element integrated with a semi-transparent film, a polarized film and a total reflection device. CONSTITUTION:An optical path separation element 21 having two faces opposite to each other with the semi-translucent film 22 provided on a part of its one side having a laser light source 17, with a total reflection film 23 provided on the other side and with a polarization film 24 reflecting an S polarized light and transmitting a P polarized light formed between the total reflection film 23 and the semi-translucent film 22, is provided on an optical path through which a light irradiating from the laser light source 17 goes to an optical information recording medium 19. The photodetectors 26, 27 are disposed on the optical path (S,P) of a reflected light from the optical information recording medium 19 separated by the polarized film 24 of the optical path separation element 21. Thus, the entire optical system is miniaturized and reduced in weight, the S/N is improved and excellent signal detection is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical information recording and reproducing apparatus that records and reproduces information using reflected light from an optical information recording medium.

2. Description of the Related Art An example of a conventional optical information recording/reproducing apparatus will be described with reference to FIG. Light emitted from a semiconductor laser 1 as a laser light source is collimated by a collimating lens 2, beam-shaped by a beam shaping prism 3, transmitted through a half mirror 4, reflected by a total reflection mirror 5, and then reflected by an objective lens 6. The light is focused and irradiated onto the surface of a magneto-optical disk 7 serving as an optical information recording medium. The reflected light whose polarization direction is tilted and read by the Kerr effect according to the signal state recorded on the second magneto-optical disk 7 is then reflected by the half mirror 4 and guided to the signal detection optical system 8. The light guided to the signal detection optical system 8 has its polarization direction tilted by 45 degrees by a 172-wavelength plate 9, and the triangular prism 1
The light is focused by the condensing lens 11 bonded to one side of the triangular prism 10, and is polarized and separated by the polarizing film 12a formed on the surface of the parallel plate 12 bonded to the other side of the triangular prism 10, resulting in reflected light and transmitted light. The light is separated into two light beams. The reflected light is detected by the first two-split light receiving element 13, while the transmitted light T is reflected by the total reflection film 12b formed on the other surface of the parallel plate 12 and is detected by the second two-split light receiving element 1.
Detected at 4.

In this case, in order to detect a focus error signal, a Naifezi prism 1 is placed on the optical path between the transmitted light T reflected by the total reflection film and directed toward the second split light receiving element 14.
5 is arranged so that a part of the transmitted light T is blocked (cut). In addition, a neutral density filter 16 is provided on the optical path between the reflected light reflected by the polarizing film 12a and the first two-split light receiving element 13 so that the amount of light equivalent to the amount of light that is blocked is attenuated. is located. Therefore, with this, the magneto-optical signal can be determined from the difference in light intensity between the reflected light and the transmitted light T. Further, the focus error signal can be detected using the well-known Knifezi method, and the track error signal can be detected using the well-known bush-pull method.

Problems to be Solved by the Invention By using the device as described above, it is possible to arrange the first two-part light receiving element 13 and the second two-part light receiving element 14 on the same substrate. It becomes possible to reduce the size of the entire optical system including the system 8. However, in the case of the signal detection method 20, in order to detect the focus error signal, the Knifezi prism 15 is disposed in the optical path to reduce the light, resulting in poor light utilization efficiency. This also lowers the signal detection sensitivity, resulting in a reduction in S/N. Furthermore, in this case, in order to adjust the amount of light attenuated by the Naifetsuj prism 15, a neutral density filter 16 must be provided in the optical path of the reflected light, which requires extra parts. This results in high costs.

Means for Solving the Problems In order to solve these problems, the present invention focuses light emitted from a laser light source using an objective lens to irradiate a light spot on the surface of an optical information recording medium. In an optical information recording and reproducing apparatus for recording information, etc., the laser light source is provided with two surfaces facing each other on an optical path between which light emitted from the laser light source is directed toward the optical information recording medium. A semi-transparent film is formed on a part of the surface located on the opposite side, and a total reflection film is formed on the other surface, and the surface between the total reflection film and the semi-transmission film reflects S-polarized light and transmits P-polarized light. An optical path separation element having a film formed thereon was provided, and a photodetector was disposed on the optical path of the light reflected from the optical information recording medium and separated by the polarizing film of the optical path separation element.

Further, the substrate including at least one of the two opposing surfaces of the optical path separation element was formed into a wedge prism shape.

Function: Therefore, by providing an optical path separation element in which a semi-transmissive film, a polarizing film, and a total reflection film are integrated, an optical component (knife It is no longer necessary to newly install a Tsuji prism or neutral density filter in the optical path, and this reduces the number of parts, making it possible to make the entire optical system smaller and lighter. Therefore, good signal detection can be performed without reducing detection sensitivity.

Furthermore, by forming the substrate including at least one of the two opposing surfaces of the optical path separation element into a wedge prism shape, it is possible to further improve the separation of the emitted light and the reflected light from the optical information recording medium. Furthermore, since the spot interval between the two lights detected by the photodetector after polarization separation can be arbitrarily set, it is possible to further reduce the size of the device and optimize the design.

Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 3. The light emitted from the semiconductor laser 17 as a laser light source is focused by an objective lens 18 and is directed to a magneto-optical disk 19 as an optical information recording medium. An optical path splitting element 21 having the following structure is disposed. A half mirror 22 as a semi-transparent film is provided on a part of the surface of the optical path separation element 21 located on the side where the semiconductor laser 17 is provided.
(for example, can be produced by vapor depositing Cr or the like) is formed, and a total reflection film 23 is formed on the other surface. In addition, these total reflection films 23 and half mirrors 22
A polarizing film 24 that reflects S-polarized light and transmits P-polarized light is formed on the surface sandwiched between the two. Then, the reflected light 25 from the magneto-optical disk 19 passes through the optical path separating element 2.
On the optical path of the light separated into S-polarized light and P-polarized light by the polarizing film 24 of No. 1, three-divided light receiving elements 26 and 27 as photodetectors are arranged.

In such a configuration, the light emitted from the semiconductor laser 17 is irradiated onto the half mirror 22 formed on one surface of the optical path separation element 21 in a diffused state. The light reflected by the half mirror 22 enters the objective lens 18, and is condensed by the objective lens 18 to form a light spot, which is then irradiated onto the surface of the magneto-optical disk 19. Then, the state of the signal recorded on the magneto-optical disk 19 is read, that is, the polarized light is rotated by the Kerr effect and becomes reflected light, which returns to the half mirror 22 of the optical path separation element 21 again.

As a result, half of the reflected light 25 passes through the half mirror 22 and proceeds through the optical path separation element 21, and is polarized and separated by the polarizing film 24 into S-polarized light (reflected light) and P-polarized light.
It is separated into polarized light (transmitted light). Note that the polarization direction is S when the light from the semiconductor laser 17 directly enters the polarizing film 24.
The light intensity of the polarized light and the P-polarized light are set in advance to be equal. By setting like this,
There is no need for a 1/2 wavelength plate as used in the prior art, which allows the number of parts to be reduced.

Then, the S-polarized light reflected by the polarizing film 24 is directly emitted from the optical path separation element 21 to the outside, and is received by the three-split light receiving element 26. On the other hand, the P-polarized light that has passed through the polarizing film 24 is totally reflected by the total reflection film 23, and the P-polarized light passes through the polarizing film 24 again.
The light is transmitted to the outside and is received by the three-part light receiving element 27.

In this case, the shapes of the two three-part light receiving elements 26 and 27 are as shown in FIGS. 2(a) and 2(b). Thereby, the focus error signal can be detected by the well-known beam size method, and the track error signal can be detected by the well-known bush-pull method. The magneto-optical signal, which is a reproduced signal, is transmitted to these two three-part light receiving elements 26.2.
It can be detected by finding the difference between the amounts of light of each of 7. In addition, other signal detection methods include:
A focus error signal can also be detected by utilizing astigmatism that occurs in S-polarized light or P-polarized light. However, in this case, as shown in FIGS. 3(a) and 3(b), photodetectors 26 and 27 are used, one of which is divided into four parts and the other part of which is divided into two parts.

As described above, by providing the optical path separation element 21 in which the half mirror 22, the polarizing film 24, and the total reflection film 23 are integrated, the number of parts in the signal detection optical system can be reduced compared to the conventional one. , which makes the entire optical system smaller.
Weight reduction can be achieved. Further, since there is no need to adjust the amount of received light as in the conventional case, there is no possibility of a decrease in light utilization efficiency. Therefore, from this point of view, it is possible to obtain a device with a high S/N ratio and compatible with higher speeds.

Next, a second embodiment of the present invention will be described based on FIG. 4. In this case, a substrate 28 including one of the two opposing surfaces of the optical path separation element 21 is formed into a wedge prism shape.

That is, here, the substrate 28 including the surface on which the half mirror 22 located on the semiconductor laser 17 side is formed has a wedge prism shape. The separation from the reflected light 25 from the magnetic disk 19 can be further increased, and as a result, the half mirror 2
Since the distance between the polarizing film 2 and the polarizing film 24 can be reduced, it is possible to further reduce the thickness and weight of the optical path separation element 21.

Next, a third embodiment of the present invention will be described based on FIG. 5. Here, the substrate 3o including the surface on which the total reflection film 23 of the optical path separation element 21 is formed is also formed in the shape of a wedge prism. As a result, the spot spacing between the two lights, the S-polarized light and the P-polarized light, which are polarized and separated by the polarizing film 24 can be set arbitrarily, thereby increasing the degree of freedom in the layout of the photodetector placement positions. becomes possible.

Next, a fourth embodiment of the present invention will be described based on FIG. 6. In the embodiments described so far, the optical path separation element 21 is
Both include a half mirror 22, a polarizing film 24, and a total reflection film 2.
However, here, the substrate 28 on which the half mirror 22 is formed and the substrate 30 on which the polarizing film 24 and the total reflection film 23 are formed are separated. It is composed of Two like two boards 28
By separating the substrates 28 and 30 and arbitrarily setting the spacing and inclination of the substrates 28 and 30, it is possible to create a layout that makes the entire optical system even more compact and easier to assemble.

Effects of the Invention The present invention provides an optical path splitting element in which a semi-transmissive film, a polarizing film, and a total reflection film are integrated. It is no longer necessary to newly install components (such as a Naifetsuzi prism or neutral density filter) in the optical path, and this reduces the number of components, making it possible to make the entire optical system smaller and lighter. Moreover, since this does not cause a decrease in light utilization efficiency, the S/N ratio can be improved and good signal detection can be performed.

Furthermore, since the substrate including at least one of the two opposing surfaces of the optical path separation element is formed into a wedge prism shape, it is possible to further improve the separation of the emitted light and the reflected light from the optical information recording medium. Since the interval between the two light spots detected by the photodetector after polarization separation can also be arbitrarily set, it is possible to further reduce the size of the device and optimize the layout.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention, FIG. 2 is a front view showing the state of the photodetector, FIG. 3 is a front view showing a modified example of the photodetector, and FIG. 4 5 is a block diagram of an optical path splitting element showing a second embodiment of the present invention, FIG. 5 is a block diagram of an optical path splitting element showing a third embodiment of the present invention, and FIG. 6 is a block diagram of a fourth embodiment of the present invention. A block diagram showing an example, FIG. 7 is a block diagram showing a conventional example. 17... Laser light source, 18... Objective lens, 19.
...Optical information recording medium, 21... Optical path separation element, 22.
...Semi-transmissive film, 23...Total reflection film, 24...Polarizing film, 26゜27...Photodetector Applicant Rico Co., Ltd. 1-1, %Z diagram J33 exposure

Claims (1)

[Claims] 1. In an optical information recording and reproducing device that records information by condensing light emitted from a laser light source with an objective lens and irradiating a light spot onto the surface of an optical information recording medium, A semi-transparent film is formed on a part of the surface located on the side where the laser light source is provided, and has two surfaces facing each other on the optical path where the light emitted from the laser light source heads toward the optical information recording medium. A total reflection film is formed on the other surface of the optical information recording medium, and an optical path separation element is provided on the surface between the total reflection film and the semi-transmission film and a polarization film that reflects S-polarized light and transmits P-polarized light. 1. An optical information recording and reproducing apparatus, characterized in that a photodetector is disposed on an optical path of light from which reflected light is separated by the polarizing film of the optical path separation element. 2. The optical information recording and reproducing apparatus according to claim 1, wherein the substrate including at least one of the two opposing surfaces of the optical path separation element is formed in a wedge prism shape.